The present invention pertains to a boot for receiving a block or tie that supports a rail of a railway track system.
Over the last few decades, a number of light rail, metro and railway lines around the world have been equipped with various non-ballasted track systems in order to reduce maintenance costs and increase performance. Certain such systems comprise a block or tie generally made of concrete, a boot generally made of molded rubber that receives the block or tie, and a resilient elastomeric pad placed between the base of the block or tie and the base of the boot. The boot is then encased in concrete or grout. The block or tie as well as a boot wall are sloped in order to permit the replacement of these components without the need to break-up the encasement concrete or grout. While these systems have performed satisfactorily over the years, it became apparent that their dynamic to static stiffness ratio increased as a vertical movement of the block or tie, and therefore the deflection of the resilient pad under dynamic loading, was impeded by an interface between the block or tie and the boot wall. This interface is a phenomenon known as the wedge effect.
A method implemented in the past to decrease the dynamic stiffness of the track system has consisted of first assembling the track system, then lifting the block or tie out of the boot, then installing a second resilient pad on top of the original pad, and then re-inserting the block or tie into the boot on top of the second resilient pad. This method was primarily aimed at reducing the stiffness of the system by increasing the pad thickness, but had the indirect consequence of eliminating the wedge effect within a range determined by the slope of the block or tie and the boot wall, and the thickness of the second resilient pad.
While the use of the second resilient pad eliminated the wedge effect, and thereby decreased the dynamic to static stiffness ratio, it also reduced the. effective embedment depth of the block or tie in the encasement concrete or grout, and thereby negatively affected the lateral resistance of the track. Also, the cost of the steps involved in providing the second resilient pad has limited the implementation of that method to only a few, mostly experimental applications.
The primary object of the present invention is to eliminate the aforementioned wedge effect while not reducing the lateral resistance of the track.
In accordance with the present invention, there is provided a boot having fins protruding from a wall of the boot. The dimensions of the fins determine the range in which the wedge effect will be eliminated. Elimination of the wedge effect allows free vertical movement of the block or tie, and full designed deflection of the resilient pad under dynamic loading within the predetermined range, once the fins have been crushed or abraded by the block or tie. Accordingly, the dynamic to static stiffness ratio of the track system is reduced, thus enhancing the ability of the track system to meet dynamic to static stiffness ratio limitations that are frequently specified in order to control related noise and vibration transmitted to the environment from the track system.
The present invention eliminates the wedge effect without reducing the effective embedment depth of the block or tie in the encasement concrete or grout, and thereby without negatively affecting the lateral resistance of the track.
The present invention achieves the aforementioned objective in an economic manner through the incorporation of fins into the boot, rather than through the implementation of costly successive construction steps and the addition of a component such as a shim or second pad to the system.